1. Field of Invention
This invention relates to a semiconductor laser wavelength stabilizer for stabilizing the wavelength of a semiconductor laser by causing same to accord with the absorption line of atoms and molecules, and more particularly, to improvements in such stabilizers.
2. Description of the Prior Art
FIG. 1 is a block diagram of a conventional semiconductor laser wavelength stabilizer, wherein modulation signals, having a frequency fm, are overlapped with an electric current supplied to a semiconductor laser LD, thereby to modulate the oscillation wavelength of the laser output. One flux of light split by means of a beam splitter BS is applied to an absorption cell CL, wherein is enclosed a standard substance which causes absorption at a given wavelength. Another flux of light split by the beam splitter BS is reflected by mirror M and then becomes the output light. The light emerging from the absorption cell CL is detected and converted by photodetector PD into electric signals. The thus converted signals are then synchronously rectified at a frequency fm by means of lock in amplifier LA. It is feasible to lock the wavelength of the semiconductor laser to the absorption line of the atoms which are present in the absorption cell CL by controlling the electric current supplied to the semiconductor laser LD so that the output signals from lock in amplifier LA come to a specified value by a control means CT.
In the conventional semiconductor wavelength stabilizer, the frequency of the output light of the semiconductor laser is locked by the absorption line of the standard substance, thereby causing the mean frequency to have stability. However, in frequency invariably undergoes fluctuations at the modulation frequency fm. This leads to instability of the instantaneous value of the oscillating frequency.